The long term objective of this research is to determine how eukaryotic cells regulate the process of premeiotic DNA replication and couple it to other events in meiosis. Failure to properly regulate meiosis can lead to improper segregation of the genetic material, and inviable or damaged gametes, which can result in birth defects. This work exploits the genetics of a simple eukaryotic organism, the fission yeast, Schizosaccharomyces pombe. The insights gained from studying cellular phenomena from simple genetic systems are helpful in describing the events occurring in complex organisms, including man, and because the process of meiosis is common to all sexually developing eukaryotes, there is a good chance that many elements will be conserved. The specific aims of the proposal are as follows. First, the degree of overlap between regulation of mitotic and meiotic DNA replication will be assessed. Genes known to be required for S phase in vegetative cells, or for coupling replication to other cell cycle events, will be analyzed for their role in meiosis. The response of meiotic cells to DNA damage will be determined, and the requirement for identified origins of replication in premeiotic DNA synthesis will be assayed. This will provide a partial description of the events of meiotic S phase as well as tools to analyze it further. Second, new genes specifically affecting premeiotic DNA replication, or the coupling of premeiotic DNA replication to downstream meiotic events will be isolated. Finally, molecular, biochemical, and genetic analysis will be carried out on the new loci identified to establish the network of trans-acting regulators that preserves the order of events in meiosis. This will allow a thorough description of the regulation of premeiotic DNA replication in a model eukaryote.